Enameling is glass fused to metal at high heat. Vitreous enamels are finely ground glass, like fine sand (or even more finely pulverized and mixed with an oil or adhesive). They may be opaque or transparent; their colors come from the use of various oxides.
Enamels are similar to ceramic glazes, except that, whereas glazes are in a raw state when applied to ceramics and go through chemical changes in the firing process that smelt them into glass, enamels have already been smelted. The firing...

Learn About Glass Enameling
It could have been so simple...but it wasn't! Until recent times (about 1800), permanent enamels had to be fired on glass vessels by an amazingly laborious process, shown here. Today, the process really is as easy as it looks.
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